In a use-case diagram, use cases (bubbles) provide a functionality to an actor. For example, ecommerce site, actor "shopper" could use bubble "browse catalog" or "make payment".
In this case, should a bank in an ecommerce example like above be considered an actor? I think not, since the bubble "make payment" does not provide any functionality for bank. On the other hand, bank is involved in "make payment" as CC information is validated by bank.
Please help me understand. I have already seen posts like Actor in Use Case diagram
but it is not clear to me. Note I am not talking about use cases that have primary and secondary actors, I am talking about use case diagrams only.
PS. There is a main difference between my case and the post link above. The question there is about ATM, so naturally it would work with a bank actor. But in my case, E-commerce site only communicates with bank.
A similar example in my case would be an insurance company and hospital software. To register a patient, insurance must be verified with insurance company, but I am not sure if insurance would be an actor for my hospital softare.